Peak or overload indicator for speech circuits



J. B.- MOORE 2,050,852 PEAK OR `OVERLOAD INDICTOR. FOR SPEECH CIRCUITS Aug. 1l, 1.936.

Filed Dec. '7, 1932 .lllllll. llllll |||||l lll KI Ill. llllll Illll IIIIIIIIIII Patented Aug. 11, 1936 PEAK B OVERLOAD INDICATOR FOR SPEECH CIRCUITS John B. Moore, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware 1 Application December 7, 1932, Serial No. 646,082

6 Claims. (Cl. 177-311) l with special regard to speech communication circuits, it should be distinctly understood that the invention is not limited thereto since the principles thereof are equally applicable to telegraphy, and to other and different types of circuits which have need fcr indicators, but which may have no direct bearing on the transmission of intelligence.

Referring to the drawing, there is illustrated a. y

radio transmitter arrangement comprising audio frequency amplifier equipment 2 connected on one side to an input circuit I and on its output side to transmitter equipment 4 and antenna 5 and also to a circuit I3 which is adapted to feed the signal waves to the indicator circuit 1, shown within the dotted lines. Input circuit I may be any suitable speech circuit or telegraph circuit whose voltages, which exceed a predetermined value dependent upon the biasing potential of the grid controlled glow discharge tube I0 to be described later, it is desired to indicate.

An important feature of the indicator circuit4 is the grid controlled glow discharge tube Ill` which is adapted to trip off and pass current upon the receipt of a wave whose voltage or amplitude exceeds the voltage value for which the grid I5 L10 is biased. The biasing of this grid may be regulated to any desired value by means of the potentiometer arrangement II and variable rheostat 8. Glow tube I0 consists of a hot cathode I6, a grid I5 and an anode Il, the Whole being enclosed in an envelope within which there is a small amount of inert gas. A characteristicof this tube is that once an arc has been started therein by the application of a positive potential to the grid, which is-of sufficient value to overcome any predetermined biasing potential, the grid loses. control oi' the tube and the arc or glow produced can then only be stopped either by removing the anode voltage or else reducing same to a value below the critical value necessary to continue the glow. A

detailed description of such glow tube is given in an article by Dr. A. W. Hull entitled Hot cathode thyratron in the July 1929 issue of the General Electric Review, pages 390 to 399 inclusive.

In the output circuit of tube I0 and connected' to the anode thereof is any suitable indicator de- 5 vice I8 which is connected with a make contact 23 of a relay I9, the break contact 24 of which-is vin circuit with the control grid 20 of a vacuum tube 2| whose anode 22 is serially connected to the energizing winding 25 of relay I9. Normally, l0 vacuum tube 2| is arranged to pass current and to operate relay I9 so that armature 28 touches contact 24 in the manner shown in the drawing. Indicator device I8 may beany desired arrange ment, such as a lamp as indicated, a meter, or an l5 alarm.

' In the grid circuit of vacuum tube 2I and associated with the break contact 24 of relay I9 is a resistance-capacity circuit, comprising resistances R1 and R2 and condenser C, this vcircuit 20 having a time constant of several seconds. The circuit is designed normally to bias the grid of tube 2| to permit the flow of current in the anode circuit thereof. In a practical embodiment of this invention a two megohm resistance was used 25 for R2 and a two microfarad condenser for'C.

The advantage of this time constant arrangement is that there may be obtained an indication y lasting any desired length of time even though the peak of the input voltage has a duration of but 30 a small fraction of a'second. Hitherto, devices which have beenused for indicating voltages in speech circuits have had the disadvantage of being either too slow to respond to these peaks of such short duration or giving an indication only 35 for the length of time that the voltage ls above a. certain value.

In the operation of the circuit, the receipt of any message wave in the input circuit I which produces a signal pulse in circuit I3swhose volt- 40 age is of the desired polarity and vwhose peak overcomes the negative biasing voltage applied to the grid of glow tube I5, will raise the grid 2l whichis suliicie'nt to lower the voltage Orl/'the 50 grid 20 an amount necessary to cut oi the anode current flowing throughgthe vacuum tube andv through the winding 25 of relay I9, Relay I9 will, of course, then release and permit armature l8 to engage contact 23, thus closing a circuit 55 to actuate indicator llt, which may be traced from the positive terminal of source 2t through the indicator lamp it, resistance 2l, make contact 23, and armature 28 of relay lil to the negative terminal of source 25. Indicator i8 will remain operated until relay 09 is again actuated. It will thus be seen that the contacts of relay t@ will not only break the anode supply to the thyratron lll and permit the glow tube circuit to return to normal but also operate indicator device i8. Condenser C will charge up with a negative potential which can only leak oi through the slow time constant circuit. This Anegative charge on the condenser and grid circuit 2@ of, vacuum tube 2l will gradually leak oi after a period of perhaps two or three seconds, during which time relay i9 remains unenergized. After this 'period the cur rent through vacuum tube 2l will again flow, thus causing the re-energization of the relay I9 through its winding '25 and a return to the normal operative position of the armaturey 23 against the break contact 2li, at which time voltage is again supplied to the anode il of the glow tube l0. The device is now ready to respond to another peak of input voltage.

The arrangement just described may be used with excellent results in conjunction with a volume indicator of the usual type as employed in broadcasting and radio telephone systems wheretelephone-transmitter to be kept up to the maxi.

mum permissible value without the danger of serious overloading on instantaneous peaks.

I claim:

1, In combination, a glow discharge device hav ing a cathode, a grid, and an anode, the glow in said discharge device being arranged to strike upon the application of a positive potential of predetermined value to the grid thereof, an input circuit coupled to said grid, an output circuit including a source of potential and the contacts of an electromagnetically operated circuit interrupter connected ,tosaid anode, an indicator, and a vacuum tube having its control electrode in circuit with the output of said glow tube and its anode in circuit with the coil of said interruptor, said tube being vresponsive to the ow of current in said output circuit for controlling said interrupter to break said output circuit and to operate said indicator.

2. In combination, a glow discharge device `having a cathode, grid and anode, the glow in said discharge device being arranged to strike upon ing a cathode, grid and anode, the glow in said discharge device being arranged to strike upon v aosoeca the' application of a positive potential of predetermined value to the grid thereof, an input circuit coupled to said grid, an output circuit including a source of potential connected to said anode, an indicator, a normally operated relay having an energizing Winding, an armature and a make and a break contact, said source of potential being connected to said armature, a vacuum tube normally arranged to pass current having a control electrode and an anode, said control electrode being in circuit with the output of said glow tube and with said source of potential through the break contact and armature of said relay, said anode of the vacuum tube being in series circuit with the winding of said relay, and said indicator being connected on one side to one terminal of said source of potential and on the other side to the make contact of said relay whereby engagement of said armature with said make contact will actuate said indicator from said source, said relay being responsive to a cessation of current ilow through the anode circuit of said vacuum tube for disconnecting said source of potential from the control grid ofv said vacuum tube and for connecting said source to having a cathode, grid and anode, the glow in said discharge device being arranged to strike upon the application of a positive' potential of predetermined value to the grid thereof, an input circuit coupled to said grid, an output circuit including a source of potential connected to said anode, an indicator, an electron discharge device reiay comprising an electron discharge device in circuit with a normally operated electromagnetic circuit interruptor, said relay being connectedv to said output circuit, said electron discharge device being responsive to a flow of current in said output for interrupting the current in said electromagnetic interrupter and for opening said output circuit, whereby said source of potential is connected to said-indicator for operating same.

6. In combination, a glow discharge ldevice having a cathode, grid and anode, the glow in said discharge device being arranged to strike upon the application of a positive potential of predetermined value to the grid thereof, an input circuit coupled to said grid, an output circuit including a source of potential connected to said anode, an indicator, means in circuit with said output and responsive to a ow of current therein for interrupting said output circuit and for connecting said source of potential to said indicator for operating same, and a time constant circuit for prolonging the interruption of said output circuit and the actuation of said indicator, said time constant circuit comprising a resistance in shunt with a condenser connected to said means.

JOHN B. MOORE. 

